本番環境で、`public/packs/manifest.json`の中身がないと言われます。

bundle exec rake assets:precompile時に生成された、public/packs/manifest.jsonの中身がないと言われます。
本番環境のみで、ローカルでは問題有りません。

bash
1Jul 18 10:42:53 AM  [301cc4fd-cc01-495c-8903-202c0f9c66ad] ActionView::Template::Error (Webpacker can't find application in /opt/render/project/src/public/packs/manifest.json. Possible causes:
2Jul 18 10:42:53 AM  1. You want to set webpacker.yml value of compile to true for your environment
3Jul 18 10:42:53 AM     unless you are using the `webpack -w` or the webpack-dev-server.
4Jul 18 10:42:53 AM  2. webpack has not yet re-run to reflect updates.
5Jul 18 10:42:53 AM  3. You have misconfigured Webpacker's config/webpacker.yml file.
6Jul 18 10:42:53 AM  4. Your webpack configuration is not creating a manifest.
7Jul 18 10:42:53 AM  Your manifest contains:
8Jul 18 10:42:53 AM  {
9Jul 18 10:42:53 AM  }
10Jul 18 10:42:53 AM  ):

cat public/packs/manifest.jsonでファイルの中身をみるとちゃんとあります。

json
1$ cat public/packs/manifest.json
2
3{
4  "application.css": "/packs/css/application-b673e020.css",
5  "application.js": "/packs/js/application-0777f7a506acd75b1bfd.js",
6  "application.js.map": "/packs/js/application-0777f7a506acd75b1bfd.js.map",
7  "entrypoints": {
8    "application": {
9      "css": [
10        "/packs/css/application-b673e020.css"
11      ],
12      "js": [
13        "/packs/js/application-0777f7a506acd75b1bfd.js"
14      ],
15      "js.map": [
16        "/packs/js/application-0777f7a506acd75b1bfd.js.map"
17      ]
18    }
19  }
20}